368 General Notes. 
EMBRYOLOGY. ! 
RUDIMENTS OF TRUE CALCIFIED TEETH IN THE YOUNG OF 
ORNITHORHYNCHUS. *—Mr. E. B. Poulton, in a brief communication 
to the Royal Society, announces the discovery of the germs of true 
calcified teeth in the young of the Duck-bi?l, of 8.3 centimetres in 
length. The sections had been prepared by Professor W. N. Parker 
for Dr. W. K. Parker, who very generously placed them at the dis- 
posal of Mr. Poulton, and also urged the latter to publish the account 
of his discovery, offering, in addition, still other materials, not only 
of Ornithorhynchus, but also of Echidna. Dr. Parker had laid the 
sections in question aside for a time (owing to the pressure of other 
work), to eventually make use of them for the purpose of studying 
the skull, when Mr. Poulton borrowed the preparations for the pur- 
pose of continuing his studies on epidermic structures—with the 
result announced; and under the circumstances his association 
with this discovery is, therefore, purely accidental ;—yet every true 
naturalist will appreciate the rare generosity of spirit which Dr. 
Parker has shown in allowing the independent publication of the 
results. 
Tooth-germs, or, rather, young not-yet-erupted teeth, were found 
in both jaws; and they were found in such a position as to indicate 
that they probably represent some part of the molar series in the 
higher mammals, Examining the sections from the front backwards, 
the first tooth appeared a little behind the anterior margin of the 
epithelial elevation, which seems to represent the developing horny 
plate, which, in the adult, is the functional representative of true 
calcified teeth. The teeth seem to form a tolerably straight line, 
extending internally to the horny plates, and passing considerably 
further backwards than the latter. Owing to imperfections in this 
part of some of the sections, the author could not determine the exact 
number of teeth with accuracy ; but they appear to be five or six In 
number on each side. The most anterior tooth-germ is different 0 
character from the others, and is apparently separated from them by 
an interval which is longer than in other cases. This anterior tooth 
is the most developed, and its apex extends so far towards the sur- 
face of the oral mucous membrane that it nearly touches the epi- 
thelium. Itisa pointed cylindrical tooth, directed vertically down- 
wards. The four or five posterior teeth are of uniform ree te 
The structure of the enamel-cap is éntirely normal, except that 
capillaries are present in the middle membrane (reticulum), intrud- 
ing from without. The inner layer of long enamel-cells is very 
1 Edited by Prof. Jno. A. Ryder, University of Penna., Philadelphia. 
2 Proc. Royal Society. Vol. XLIII, 1888, No. 263, pp. 353-356. 
